Telephone system



- Jan. 9, 1940. c. E. BEAL-Er m.

TELEPHONE .SYSTEM Filed March 26, 1938 7 Sheets-Sheet .1

To [0cm E/iurom XCHANGF CHARLES EDMUND BEALE ZlDR/S TREVfl/Q RICHARDSJan. 9, 1940. v c. E. BEALE 1- AL 2,186,317

TELEPHONE SYSTEM Filed March 26, 1938 7 Sheets-Sheet 2 w 9 1F'1 Z. QUII}f 034)) by!) lib yl/ )1?! C HARLES EDMUND BEALE 101 215 TREVOR R/CHARArrx Jan. 9, 1940. c. E. BEALE- ET A1.

TELEPHONE SYSTEM Filed March 26, 1938 7 Sheets-Sh eet 3 )exl #1 1 w i i-UFO - rwl/ /f 1:? i-

' INVENTORS CHARLES EDMUND BEALE //DP/$ TR Val? RICHARDS Jan. 9, 1940.c. E. BEALE- ET AL v 2,186,317

TELEPHONE SYSTEM Filed March26, 1938 7 Sheets-Sheet 4 CHARLES EDMUNDBEALE Z IDR/S TREVOR RICHARDS ATTY ") '3 e f/W Wield Ill/HTf/f Jan. 9,1940.

Filed March 26, 1938 '7 Sheets-Sheet 5 DDM IN VEN TOPS CHARL E5 EDMUNDBEALE I lDR/S TREVOR RICHARDS c. E. BEALE ET AL 2,186,317

TELEPHONE SYSTEM Jan. 9, 1940.

c. E. BE AL E -r AL 2,186,317

TELEPHONE SYSTEM Filed March 26, 1938 v-sheeis-sheet e s6 F' 3 15' B H-4' M WQ /AI VE N T0125 CHARLES EDMUND BEALE Z IDR/S TREVOR RICH/U705?1940- c. E. BEALE. ET AL 5,

TELEPHONE SYSTEM Filed March 26, 1938 7 Sheets-Sheet 7 i I $53REGULARIKOUTE j (i /7332i;

AGE a ALTEFTWWE 3' if? A A z 7 5% m" fn z-z v ge I. 7 g "INS M M 5 v40NW5 REGULAR RoufE 9e4 1'55 In D INVENTORS C HAPLES EDMUND BEALE [DR/5TDBEVOR RICHARDS PatentedJan. 9, 1940 UNITE "TELEPHONE SYSTEM v CharlesEdmund Beale and Elvis Trevor Richards, Liverpool, England, assignors toAssoci ated Telephone & Telegraph Company, ChicagmJlL, acorporation ofDelaware 3 Application March .26, 1938, Serial No.. 198,223

In GreatBritain April 13, 1937 11 Claims. (01. 179*27) v trunk exchangeobtain connection to thewtrunk v The present invention relates totelephone systems' and is moreparticularly concerned with socalledautomatic trunk exchange systems which employ automatic switches fortheiselection of trunk lines. The invention is particularly applicableto exchanges of the above typein which the trunk board operators areprovided with digit keys'ets on which the number of the required trunkor group of trunks is set up. In response to this an impulse sendercommon to a number of operators comes into operation in a well-knownmanner on receipt of a start signal and sends out trains of impulsestoset up the train of switches.

A system of this general type'is disclosed in British Patent No.459,803. The object of the invention is to provide an improvedkeyroperated impulse sender giving's'pecial facilities such may bedesirable in systems operating on the above described lines. l

According to one feature of the invent-ionin a telephone systememployingautomatic selecting switches for the selection of trunk lines undercontrol of a key-operated impulse rangements are, made whereby if delayworking is in force on a desired-group of trunks the I sender withholdstransmission of the keyed-up digits and returns an indicationto theoperator of the estimated 'tirn'e'of delay It should be explained thatdelay working represents the con dition when owing to congestion on aparticular route a supervisor has thrown akey or performed "-somesimilar operation "to indicate to the operators that calls over "thatroute cannot be completed on demand on a'call storage basis but mustapplication No. 1-93,415, filed March 2,1938.

befhandled'by a special-delayoperator. The "invention will bebetterunderstood from the following description of one methodoi carrying itinto effect, referencev being had to the accompanying drawingscomprising Figs.- l-l.

.. Fig. l is a trunking diagramshowing in schematic I iormthe trunkingarrangements' at atypical I automatic trunk exchange while Figs/2 7which should be arranged in the manner indicatedat the bottom of Fig. 5{to form one complete dia gram, show the circuits of aseven-digitimpulse sender with alternative routing anddelay testingfacilities- The two-motion switch employed in.

the sender is assumed to be of the'twmmagnet type as disclosed in thepatent to Saxby No. 2,028,689, andv has so-called rectangular motion,while the uni-directional switches employed are of the. well-knownreverse drive 'step-by-step j type.

Considering .first the trunking diagram,.Flg. l,

rautomaticsubscribers. in.- the area local to the sender,-ar- 3 group oftrunks and :the second digit determines whether hunting shalletake placeor whether: an individual trunk in thegroup shall be selected.

Four" digits must thereforeb'e keyed up to obtain exchange by dialling;In responsegtoithis a two-motion, switchv CCF terminating the incominglineILL is causedito'hunt for'an idledemand operators po'sitionDP. Whenan'idle position is:

foundjthe connection is extended over the connecting circuit CC. andpthepositionhcirlcuitiPC and the operator speaks to the callingparty,

records particulars Oft'll call'and. then. operates a key in order toconnectg-with a first; selector:

which on seizure engages a free-Q sendertsvover a huntingswitch SH. q

. It will be seen that access'can be had-to the 0nd and third selectorsSi S2 and S3 respectively are of the two-motion type; the switches:S3.hav-'- .ingxdirect. access to; groups of outgoing. trunk lines andbeing of the two-digit:type that is to sayythe first digitreceived.servesto select a train of trunk selecting switches Si S2 and S3 vonlyover the 0 level of the, first selector Si, the

for outgoing relay sets suchan OGR to, the'local I access .to agroup-of. trunks and O'must befkeyed 'as a first" digit.Theuthird-selector.mayihave .facilities forcall storage as. describedinour pending application No.. 193,414, :filed; March 2,-

1938, or alternativelythey vmay .have-iiacilities' for-repeating testingoi a trunk group until a free trunk is found'as describedinourpendingThe operator now keys .up the routing digits firstdigit whereupon a;circuit change isbrought about in the sender so that after the keying.up"

of the second and third digits in the number to select a particulargroup of. trunksgan auxil-,

iaryswitch AS in: the sender iscaus'ed to search for markings appliedto. one ofits banlcs in ac-. cordance with these latter digits. Thisauxiliary switchis of the 160,-.o'utletztwo-motioh type and when it hasthus positioneditself. access can be had over its Wipers to a "groupbusy equipment.

such as GBE associated withthe desired group of trunks, to'a group busyequipment associated with a group of trunks which provide an alternative route to the desired distant exchange if these group busyequipments to the delay supervisors position 138.: Before the sending;outsuch a route is available,;.andalso by. way. of

of the keyed-up digits commences, simultaneous tests are made on boththe regular and alternative routes and if the regular route is free anddelay conditions are not obtaining thereon, the

keyed-up code is at once sent out while it is engaged or in delay thealternative route is tested if one is provided. If the alternative routeis free and not in delay, the alternative route code as determined bythe setting of other wipers of the auxiliary switch is sent out but ifit is busy or in delay or such a'route is not provided the call isrouted overthe regular route even if this latter route is engaged butnot if it is in delay. If the third selector is of the call storagetype, the call will then be placed in storage while if this switch is ofthe re-searching type it will perform repeated testing operations untila trunk in the group becomes free. If however delay conditions are inforce on the regular route, no sending takes place and a tone signal isreturned tothe operator indicative of the estimated time of delay.

In the case of calls incoming over a trunk line such as ITL to thethrough position TP at which the equipment is substantially the same asthat at the demand position, the first digit keyed may be other than 0in order that an incoming call from a distant exchange may be routed tothe local metropolitan automatic exchange. Since the first digit isother than 0, the auxiliary switch in the sender is not set intooperation as it is not required and the keyed-up code is therefore sent.

out as soon as the operator depresses her start key.

Referring nowto Figs. 2-7, the detailed circuit operation of the senderwill be described. On the seizure of the sender equipment, earth appliedby way of a relay in the first selector over the SW lead operates relaySW, Fig. 5, which thereupon operates relay B, Fig. 6, over its lowerwinding. Relay Bv at armature bl earths a common operating and "holdinglead i5, at armature b2, Fig. 5, returns a guarding and holding earthover the incoming P conductor and at armature b6, Fig. 3, extends anearth from wiper DD! in position 1 to energise the distributor switchmagnet DDM, Fig. 5, in series with relay 'BP, Fig. 6, the function ofwhich will be dealt with later in the description. The magnet nowinteracts with its interrupter contacts 11112 to advance the wipers toposition 2 where relay BA is operated by way of its left-hand windingfrom the same wiper and bank. This relay at armatures bal and bat, Fig.2, inserts relays DSA and D83 in the incoming keying conductors IN and+IN which extend over the wipers D333 to DB6 in position 2 to relays AW,AX, AY and AZ which comprise the first set of decoding relays. It shouldbe explained that keying is effected from the operators position circuitover two wires by combinations of positive pulses and light and heavynegative pulses, and at the receiving end these pulses are directed intothe appropriate one of the available fourchannels by the use of themetal rectifiers MRA, MRB, MRC and MRD; this method is described indetail in British Patent No. 398,812. Relay BA also at armature baii,Fig. 7, earths a common operating and holding lead it and lights thesender engaged lamp LP, and at armature bat it locks over its right-handwinding.

Assuming that the sender is seized from a demand operators position andthat the number keyed is 0831, on the depression of the digit key 0 alight negative impulse is sent over the incoming positive keying leadandat the same time a posi tive impulse is sent over the incomingnegative lead. The circuits. extend by way of relays DSA and DSB,rectifiers MR3 and MR0 in conductive directions and wipers D204 and DD5in position 2 and serve to operate relay AX over its right-hand windingandrelay AY over its right-hand winding in series with the middlewinding of relay AZ, relay AZ not operating in these circumstances dueto the light nature of the pulse. Relays AX and AY thereupon look overtheir left-hand windings to lead l5 and prepare a marking correspondingto the digit 0 in the bank S4 of the sending switch Sin a manner to bedescribed. Earth is also extended from lead l5 over armatures ctzrfi,oy' and azfi to operate relay TG over its upper winding. This relaythereupon locks over its lower winding at armature tg! to the earthedlead It, prepares a self-driving circuit for the vertical magnet VM,Fig. 7, of the auxiliary switch at armature t'g3 and at armature tg5,Fig. 6, disconnects an operating circuit for the sending start relay SSwhich would otherwise be completed when the operator subsequentlydepressed the start key after the keying of the fourth digit in thenumber. By this arrangement the sender cannot start sending-out untilboth the operators start signal and a signal from the auxiliary switchare received. Meanwhile the series connected relays DSA and DSB are alsooperated due to the depression of the digit key' and energise the magnetDDM, Fig. 5, of. the distributor switch 'overarmatures dsai and dsbl. Onthe release of the key these relays restore and de-energise the magnetDDM which thereupon advances the wipers of the switch DD into posi-Ztion 3. I

The key 8 is next depressed and this results in the connection of alight negative pulse to both of the incoming keying conductors where itfinds a path by way of the series connected relays DSA:

On the depression of the digit key 3, a heavy negative pulse is appliedto the negative keying conductor and this finds a circuit by way ofrectifier MRA to bring about the operation of relays CW and OK inseries. These two relays lock in the usual manner and prepare a markingcorresponding to digit 3 in the bank S4. On the release of key 3 the DDswitch wipers are advanced to position 5.

The advancement of the DD switch wipers to the fifth position indicatesthat the required group of trunks has been selected, the fourth digitwhich is to follow merely determining whether hunting shall take placeover the whole or part of the selected group or whether a particulartrunk in the group is to be selected.- The two-motion switch istherefore now caused to search for vertical and rotary bank markingsmade in accordance with the digits keyed into the sender.

Earth is now extended from the busykey-contacts KBI, Fig. '7, overarmatures ba5, c7c5, col, [Z03 and tg3, wiper DD2 in position 5 andarmature h to operate relay FS by way of its lower winding in serieswith magnet RMand relay .BP which do not however operate in thiscondition. Relay FS upon operating locksover its upper -windingby way ofits armature fsl and completes I if a self-interrupted driving'circuitforthe vertical magnet"V-M from earth extended byway of its magnet :VMto battery viarelay BP' and accordgly the wipers areraised verticallystep-by-step. Relay FS also at armature fs8, Fig. 3; extends a:"armature' is! and'armaturespal, hrand rs2."

vertical magnet'interrupter contacts 12m, and

- battery marking potential by way of armatures of :"the second set ofdecoding relays'which have'been operated to the left-hand vertical bankVB of the two-motion switch and since in this case relays i: BW and BYhave been operated in response to the battery marking potential isapplied over armaturesbwZ, 11:02, 1122 and byii to .:..contact 8 in thevertical bank VB.

a. marking, relay PA operates quickly and. opens" the v l magnet drivingcircuit at cuit for relay RS. This relay thereupon locks H make-first"light armature rsl, at arma- "over its the vertical magnet 1 ture rs2iurtherdisconnects driving circuit and prepares a driving circuit for:the rotary magnet circuits and thus ...at armaturers l, Fig. 3, andextendsit over arma- :turers5 tothe contacts'of the third set of.decoding'relays in order that the position of the desired trunkgroupcan be marked inthe bank of 'When 'thevertical wiper VW encounters thisthe .same armature completes an operating cir- RM, at armature 1's3shortthe contacts of the second setof decoding relays wiper P.

It should be mentioned that 1 contacts on each of the levels of thisbank. are multipled together, a lead extending fromeach ofthe tensets of'multipled contacts in the bank to the armatures of the decoding relaysso that .inithis case since relays CWand CX are operat--edinresponsetothe keying o-f digit 3 the third =contacton each levelwill be marked from. the resistancebattery YB by way of armatures fsB,rrs5',.cw2 and cx2..

On the release of relay PA, a self-interrupted irdriving circuit iscompleted for the rotary magnet RM'from earth by way of and T32, faultrelease jack FRJ, off-normal con- Y ";--.first.vertical step of theauxiliary ".Lmagnet interrupter contacts Tm,

tacts N2 which were mechanically operated on the .RM to battery viarelay .BP and the wipers are "raccordingly rotated in search-ofv themarking.

On; the first rotary step the rotary off-normal springs are mechanicallyoperated and at contacts NRl, Fig. 4, relay PA'is disconnected from thevertical bank; at contacts is disconnected but remains bank DB2 and atthe same contacts an operating.

NR2, Fig. 7, relay RS v circuit is prepared for relay H while atcontacts NR3,-Fig. 4, the short-circuiting 1* from relay PA.

,When the P wiper encounters the marking,

relay PA again operates to open the magnet driving circuit andthis timeit operates relay H. ::Re-

lay I-Ithereupon further opens, the magnet drivping circuit. at armaturehl,. prepares a circuit 'for'the sending start relay SS, Fig. 6, atarma- :ture k3,. completes a locking circuit for itself over itsarmature M and also releases relay RS'which in turn releases relay PA.If the operator has -'=;not already depressed the sending startikey, no

. furtheriroperation takes place until she does so, while ifthis key hasalready been depressed armature pa! and at I I search, 1;

:..disconnects the resistance marking battery from the correspondingarmatures pal, hi

switch, rotary rotary magnet held overwiper and earth is removedrelay-SS will now operate andiinitiate thesendin out off the storeddigitstunless-it is found that delayconditions areobtaining on thedesired trunk group, as will be described later. 1

Inthe meantime the fourth digit 1' of the re quired numberwill havebeenkeyed up and in response to this a light negative pulse is transmittedover the incoming negative conductor: to "operate relay'DW. This relaylocks and pre pares a marking corresponding to digit 1 in the 10 I bank'ofwiper S4 and, at armature d103, Fig. 6,

extends an earth over armaturesdyS, (2.21, 03:06 and 914 to operate.relay AR the purpose of'which will be described later. On the release ofthe key, '2 the DD switch wipers are advanced in the normal 15 mannertoposition 6.

Since the four digits corresponding tothe required numberhave been keyedup, the operator now depresses the sending start key which affects theconnectionof alight negative pulse to the? negative keying lead and aheavy negative pulse .to the positive keying lead. In response. relaysEW,.EY and -EZ are operated over. the DD3 and CDD5 wipers in position 6and prepare a circuit'over armatures e102, e122, ezZand e114, Fig. 6,for the' Icut-ofi relay CO which is operated afterthesubsequent-transmission of the setting digits. If in theimeantime relayH has been operated thereby indicating that the two-motion switch hascomm pletedfinding, an operating circuit will be com .pletedfor relay SSfrom the earthed lead l5 by wayof armatures ew3,zey5, ez6,-e:r5, andhtto .zinitiate-the transmission of the decodeddigits.

Itwill. be appreciated that the cut-off circuit or and start circuitdescribed couldbe prepared fequally well by the operation'of a similarcombination'ofrelays many of the seven decoding sets if a differentnumber of digits-had been vkeyed. 1 If however, the full seven digits:are

keyed relays'HX and HW are utilised to respondeither. toa start signal,or in a manner to be describedlater, toa cancel signal.

Relay SSqupon operating, at'armature ssl, Fig. 6, prepares an operatingcircuit for relay IG and at armature s52, Fig. 7, disconnects theholding circuit for relay FS which'holds operated for a further 'shortperiod due to'its slug.- At a'rmatures ss5..-and ;ss5, 'Fig. 5, theincoming keying leads are disconnected and at armature ss'l, Fig. 6,earth is connected up over the CNZ wiper in position 13 to the armaturesof the first set-of decoding relays. During the release time of relay FSthe lower winding of relay GE, Fig.7, is connected over armatures s83,drjl and fs3 to the wiper R of-the two-motion switch while the upperwind ing of relay AGE'is connected over armatures ss4,

*drZ and fsl to wiper A. The banks of these wipers and also of wipersDI, D2 and RD are multipled to-the corresponding banks of the two-motionswitches of-other senders'and extend to the varif-x ous trunk group busyequipments while banks.

6 C|',.C2. and P of the two-motion switch are wired -.zindividually. ineach sender. The R, D|,I D2 and :RD bank contacts on which the wipersare now positionedextendto agroup busy equipment .as -i sociatedwith thetrunk group- 083. and if there is. an alternative routeprovided to thedesired exchange the bankcontact on which the A wiper is positionedextends to a group busy equipment associated with this route. If thereis no alter-'3 native route-provided, the A bank contact is permanently'earthed in the sender byway of' the "strap connection shown dotted. If.thetrunk g oup @083 serving-the so-called regular routeis engaged or.in :delay; wiper 'R will encounter an. earth. post 5 tential extendedfrom the associated group busy equipment and-if the alternative route isengaged or in delay wiper A will also encounter earth.

It will first be assumed that the regular route is neither engaged norin delay, in which case the R wiper will ,not pick up any potential andrelay GE will not therefore be operated. On r'elease of relay FS, thesender therefore will com- Relay FS on releasing completes a holdingcircuit for relay B over its upper winding at armature fsfi, Fig. 6, thelower winding of the latter relay being subsequentlydisconnected onrelease of relay SW when the first selector switches through to thesecond selector while at the same armature earth is extended to relay IGand to the motor-driven magnet impulse springs MIS. Relay IG, thefunction of which is to prevent the extension of a clipped impulse fromthe impulse springs MIS to the sending switch driving magnet SM, doesnot operate until the impulse springs open and when it does so itconnects them up at armature z'gi to the magnet SM. Accordingly thesending switch wipers are advanced 'step-by-step round the bank contactsandit will be noticed "that as soon as wiper S2, Fig. 5, reachesposition 3 the loop impulse springs LIS which are operated from the samemotor as the magnet springs MIS and which are closed during such time asthe magnet springs are open and vice versa, are connected across the.OUT and +OUT conductors extending to the first trunk selector so thaton each subsequent step of the sending switch an impulse is delivered tothe selector.

When ten impulses corresponding to the first digit keyed have beendelivered to the first trunk selector, wiper S4 will pick up an earthsupplied to contact l3 by way of the central switch wiper CNZ, Fig. 6,in position 1 and armatures aw'Z, ay2 and a334, Fig. 4, whereupon relaySZ, Fig. 7, operates and locks by way of armature 52! and the S3 bankand wiper to earth. Relay SZ disconnects the loop pulse springs LIS fromthe outgoing loop at armature $26 and replaces them by the winding ofrelay D, at armature 522, Fig. 6, opens the pulsing circuit to themagnet SM and disconnects relay 1G which is slow in releasing due to itsslug and at armature sad completes .a circuit for the control switchmagnet CNM.

During the release time of relay IG, earth is extended over the Si wiperand bank and armatures 2'93 and 821' to operate relay PC over its lowerwinding whereupon at armature'pc! the upper winding of this relay isinserted in the outgoing loop in order that it may hold operated whenrelay IG releases.

On the release of relay IG, the timing of a suitable interdigital pausecormnences but in addition arrangements are provided by which the lengthof this pause can be automatically adjusted in accordance with theactual time taken for a selector which has just been set to hunt for andswitch through to a succeeding selector. It will be noticed that on therelease of relay IG the lower winding of relay PC is disconnected atarmature ig3 and this relay now holds on its upper winding which hasonly sufficient turns to produce a suitable holding flux. When the firstselector completes its hunting operation and switches through, there isa momentary interruption of the loop current which allows relay PC torelease due to theinefliciency of its holding winding and it thereuponat armature pol shortcircuits its upper winding to prevent re-operationwhen the loop current is restored and completes a self-interrupteddriving circuit for the magnet SM from earth over the SI wiper and bank,armatures s23, pc2, 2'92, and 2'93, magnet interrupter contacts sm,magnet SM to battery via relay BP so that the S switch wipers arerestored quickly to the home position 1. The sending out of the nextdigit then commences.

Should relay PC fail to respond to the transient signal or should therebeno signal returned as would occur between the two digits during thesetting of a standard type of final selector switch,

the normal interdigital pause will be provided in the following manner.On release of relay IG the impulse springs MIS are again connectedacross its winding and a self-interrupted driving circuit is completedat armature 2'93 for the magnet SM from bank and wiper SI. After wiperSI has advanced beyond contact 19, the self-interrupted driving circuitis disconnected and earth is reconnected to the winding of relay IG overarmatures ssE and p02 and when this relay reoperates on the opening ofthe magnet impulse springs MIS, the sending switch is stepped over thenext group of contacts under control of these springs so that apredetermined period may be tends an earth to the armature of the secondset of decoding relays. The original operating circuit is againcompleted for relay IG at armature $22 and the sending switch Sagaincommences to step under control of the impulse springs MIS to sendout a train of eight impulses corresponding to the second digit keyed inthe same manner as the first train except that the wiper S4 on reachingposition liwill encounter a marking extended over armatures grl,fs8,-rs4, b202, 12x2, 2:22 and by3.

After the transmission of this digit, the CN wipers are advanced toposition 3 and the third train of three impulses corresponding to thethird keyed-up digit 3 is then sent out, the marking being extended overarmatures 0x2 to position 6 on the St bank.

' Before the sending of the fourth digit is described, one or two pointsin connection with the setting of the two-digit third selector in thetrunk selecting train will be dealt with. If 0 is keyed as the firstdigit, thereby indicating to the sender that the trunk selecting trainis to be utilised, it is arranged that if the fourth digit keyed is 1 anunbalance signal is transmitted in response instead of an impulse. Itwill be understood from the description of the third selector in ourpending applications Nos. 193,414, and 193,415, filed on March 2, 1938,previously referred to that by this arrangement the first outlet of eachlevel need not be wasted as would be the case if an impulse wastransmitted. On reception of this unbalancesignal thethird selectortaken into use is caused to perform a hunting operation over the wholeof the selected trunk group.

As mentioned previously, in response to the keyingupofthefourth digit 1relay DW is operated and operates relay AR. This relay thereuponatarmaturear, Fig. 5, prepares a circuit 5 "for unbalancingtheoutgoingloop after transmission of the third digit and at armature arZprepares .a circuit for quick-stepping the CN switch wipers pasttheposition 4 which they would normally occupyfor the sending of the"fourth digit;v During the sending out of the third 1 train. of impulsesthe CN switch wipers are in position 3 and hence on operation of relaySZ at the end of the train an earth will be applied over-.wiper CNI andarmatures or! and sz5.,to unbalance the-outgoing loop. This earth alsoshort-circuits and releases relay PC since the outgoing positive loopconductor connects with thejearthed winding of the distant impulsingrelay-andthe sending switch S is-therefore quickly self-driven to thehome position, When relay SZ releaseson completion of the. homing of theswitch S, theswitch magnet ,CNM is de-energized and" the wipers arethereby advanced to I thenext positiond which would be normally occu-*pied during the sending out oi an ordinary fourth digit. Since nofourth digit. is sent out however a circuit is .completedfrom theearthed wiper CNI in this position over the operated armature ,ar2 toquick-step the wipers to position 5. m: In this position earth isextended over wiper 0N2, Fig. 6, and armatures ewZ, earl, e22 and ey l Yto operate relay CO which thenlocks over its armature cozand at the samearmature removes the holding. earth from lead It thereby releasing the;decoding relays and relays B, SS and AR while at armature col, Fig. 7,the holding earth forrelay. H and for the relays associated with thetwo-motion switch wipers is removed. The release :of reiayAR atarmatures an and M2, Fig. 5, prepares a homing circuit for the controlswitch .CN while the release of relays H and SS- initiates the homing ofthe two-motion switch by the completion of a self-interrupted drivingcir-' cuit' for the rotary magnet RM from earthhover 'i5earmaturesssl,Fig. 6, f8! and b2, fault release jack-FRJ', ofi-no-rmal contacts N2,rctary'magnet interrupter contacts rm, magnet RM to battery via relay BFand the'switch wipers are accord ingly advanced to the 12th positionwhereupon socithey restore vertically under gravity and then rotateunder springxcontrol-back under the banks to'itheir full normal positionwhere the magnet'; driving circuit is openedby the cit-normal con-"remainmarked as engaged'until theidle inarkingbattery is replaced onthis lead. Relay B also at. armature magnet DDM'from the earthe'd wiper7 iotated to ahome'position l3'where the driving circuit is opened. Thenext time the'sender is taken into use the DD switchwill start from thisposition and then subsequently restore to its other home position i. Orrthe release of relay 7533A; relay TG, Fig.6, is released at armature1305,

b5','Fig.-.3,"compl'etes a self-interrupted driving circuit forthe-distributor switch and bank DD'I, armature b5, magnet interrupter.contacts. ddm, armature cki magnet DDM to battery via' relay'BPandtheswitch wipers are accordingly per visory lamp LP is extinguished, whileat armature M3, Fig. 5, a homing circuitis completed for the controlswitch CN and the wipers are thereupon rotatedto position 1. When allswitches have reached, their home position and Fig. 7, and at the samearmaturethe sender su-- relay CO has released, the idle marking batteryis replaced'on the incoming P conductor byway of resistance YA,armatures 130.4. and 27101, oftv normal contacts Nl, armature 003, keycontacts KB4 and armature b2, so that the sender now a marked as free.forfurther use.

'Cancellation of the keyed-up'digits may be effected at any time priorto the operationofthe start key by the operation of the cancel keyintheposition circuit." This results in theconnec= tion of a heavy negativepulse to both of the incoming keying. conductorsand accordingly all thedecoding 'relaysof whichever setisthen connected up are operated. RelayCK, Fig. 5, is

therefore operated over its lower winding and atarmature ckl inserts itslow resistance upper winding in thecircuit ofthe distributor switchvmagnet DDM and at armatureckfi, Fig. 3, com'- pletes a self-interrupteddriving. circuit forthis magnet in order to home the distributor switch.At armaturescki, andclc l-the incoming keying leads are'opened,atarmature 0.705, Fig. .7, theholding earth'for relay TG and other relaysis i disconnected, while atarmature c706 Fig.4,the holding earth leadtothe decoding relays is disconnected. During the homing of the DDswitch relay CK remains held over its upper lowresistance winding andwhen the switch reaches the home position. relay CK releasesand restoresthe circuit conditions in readiness for the keying-up of the correctdigits.

Returning to the point in the description where relays GE and AGE-wereconnectedto wipersR and A, it will now be assumed'that the regular routeis either engaged or in delay and that an iv alternative route isavailable which is not in' delay. Furthermore it will be assumed for areason to be described that the fourth digit keyed is 1.. During therelease time of relay FS relay GE will be operated by an earth extendedover the R wiper from the regular route group lousy equipment, butsincethe, alternative route is free and not in delay the A wiperwillencounterzno earth and hence relay AGE. will not operate. Relay .GElocks over its upper winding at armature gel and at armature ge3operates relay GR.

This relay at armatures yr! and grLFig. 3, disconnects the regular routemarkings. correspondf 22-11 ing to the second and third digits keyed andcon-' nects up in placea two-digitualternative route code which isefiected over leads I1 and I8, wip-i' ers and banks-Cl and C2 ofthetwo-motion switch and a suitable translation field TF." For example thefirst three digits 'of the keyed up number 0831 might be' changed to065; thelast digit '1 being sent out in a normalmanner as an unbalancesignalso 'as' to initiate hunting over the whole of the alternativeroute group of trunks.

If'however the fourth'digit of menumber is other than 1, therebyindicating that it is desired. either to select a particular highgrade.trunk inthe group comprising the regular route, or to cause huntingoveria sub-group of trunks there: in, the aim of the operator would bedefeated if the call was routed over an alternative route.

operated, that is to say, if 1 is not keyed upas a fourth digit, relayAGE is operated over its Accordingly it is arranged that if relay ARisznot 1 lower winding as soon as relay SS operates and this simulatesthe efiect of an engaged or in delay condition on the alternative routeso that the call will not be routed thereover if the regular route iseither engaged or in delay.

If both the regular and alternative routes are found to be busy, bothrelays GE and AGE are operated, so that relay GR is not operatedwhereupon if the regular route is not in delay, the keyed-up code issent out over this route. The call willthen either be placed in callstorage by the third selector or alternativelyif another type of thirdselector is used the trunk group will be hunted over repeatedly until afree group is found.

If the regular route group is in delay and if the alternative routecannot be utilised, that is to say, it is also in delay or engaged,relays GE and AGE will be again operated. During the release time ofrelay FS the lower winding of relay DR is connected over armatures (we land fs to the wiper RD which due to the delay condition will encounterearth extended from the group busy equipment associated with the groupof trunks serving the regular route. Relay DR therefore operates andlooks over its upper winding at armature dr3, at the same armaturedisconnects the locking circuits of relays GE and AGE, at armatures drIand (Z12 connects the lower windings of these two relays to the DI andD2 wipers respectively, at armature dr4, Fig. 5, connects the retard TRacross the incoming keying conductors in order that tone signals may bereturned to the operator and at armature dr5, Fig. 6, disconnects theearth supply to relay IG so as to prevent the sending out of thekeyed-up digits. It is arranged that the contact on which the DI wiperis resting is earthed from the group busy equipment associated with theregular route as soon as delay conditions are put in force thereon bythe delay supervisor. If the supervisor wishes to signal that there willbe an estimated delay of twenty minutes as would be determined from thenumber of dockets she is holding she will operate a so-called twentyminute delay key. If the delay is likely to be of the order of fortyminutes she throws another key and the contact on which wiper D2 isresting will be earthed instead of that engaged by wiper DI while the'earthing of the contacts engaged by both wipers DI and D2 will indicatea delay of sixty minutes. Accordingly therefore if the delay is of theorder of twenty minutes relay GE will be operated over the DI Wiperwhereupon a tone is extended over common lead II, Fig. 5, and armaturesage2 and ge2 to the right-hand winding of the retard TR, this tone thenbeing induced in the left-hand winding and extended on to the incomingkeying conductors in a balanced circuit. The operator is thus notifiedand will then inform the calling subscriber of the approximate Waitingperiod, and will release the sender and forward. the docket recordingparticulars of the wanted connection to the delay supervisor. If thedelay is of the order of forty minutes, relay AGE will be operated and adifferent tone signal will be connected to the winding of relay TR fromcommon lead I2 while if the delay is of the order of sixty minutes, bothrelays GE and AGE will be operated to connect up another tone indicationfrom common lead I I] to the right-hand winding of retard TR.

The case will now be considered in which the sender is taken into use byan operator at, a through position who wishes to extend an incoming callto a local automatic exchange. In this case the first digit keyed willbe other than 0 and hence relay TG will not be operated so that thetwo-motion switch is not started up to find a marking since it has nofunction on this class of call. On receipt of the start signal, trainsof pulses in accordance with the digits keyed are therefore immediatelysent out to route the call to the required destination. Furthermoreunder this condition since relay TG is not operated relayAR cannot beoperated in response to afourth digit 1 so that if this digit is keyedit will not be converted into an unbalance signal.

If in the setting up of a call any selector in the train, excepting thethird trunk selector, finds all outlets on a level busy, arrangementsare made to return a signal to the sender so that it may immediatelyrelease and drop out of the connection; at the same time the originatingkey-sending operator receives busy tone without having to wait until thesender has finished sending. Assuming for example that the secondselector finds all outlets busy, it rotates to'the 11th step andthereupon connects positive battery to the PS lead. This extends by wayof armature col and rectifier MRE in a conductive direction to operaterelay ZR over itsleft-hand winding, the rectifier MRE preventing theextension of an earth potential by way of this winding on to the PS leadwhich might bring about false operation in the selecting switches. RelayZR at armature zrI looks over its right-hand winding to lead I6, atarmature 22*2, Fig. 6, operates relay CO to bring about the release ofthe sender and at armature 2T3 breaks the circuit for relay SW. It willbe understood that this relay is held operated during the setting andhunting operation of the first selector only, and if this switchencounters a busy condition the operation of armature 2T3 avoids thepossibility of relay B being held on its lower winding from armature swland thus maintaining an earth on the P-lead which would bring about alock-up between the sender and this selector. On the release of relay Bin response to the disconnection of its holding circuit at armature 002,the guard and holding earth is removed from the P lead whereupon thefirst trunk selector extends its incoming leads through to the secondselector. Busy tone is thereupon transmitted from this selector by wayof the first selector to the operator.

When delay working is introduced on any of the trunk groups, an operatoris assigned to clear up the waiting dockets. Arrangements are providedwhereby she may use an ordinary position from which she may gain accessto a group in delay. For this purpose a simple strapping connection iseffected in the position circuit while a delay operator key is thrown,the strapping preventing unauthorized use of the delay operator key.When the sender is seized from such a position, in addition. to thenormal circuit operation, amomentary loop signal is extended forwardover the keying conductors and this brings about the operation of relayDO, Fig. 2 from earth applied to the positive conductor by way of thedistributor switch wiper DDS in normal position; this earth extendingover the loop and back via the negative conductor to operate relay DOover its left-hand winding. Relay DO thereupon looks over its right-handwinding to lead I5 by way of resistance YC, Fig. 5, to the PS lead;

*I'his arrangement is provided so that during the transmission of trainsof pulses a straightorder to eliminate impulse repetition, while at 'theend of the impulsing the momentary applicaoperator should key 0 as afirst digit. No mat ter what digits are keyed therefore, the sender willsend-out corresponding trains of'pulses immediately on depression of thestart key.

automatic exchange, that is to say where relay vTG is not operated,during the'release of the sender a positive battery potential is appliedby through connection maybe provided in the outgoing relay set to theautomatic exchange in tion of the positive battery signal over the'PSlead will bring about the insertion of the WBi1-' known'D and Isupervision bridge in this relay set, so that the loop" supervisionfromthe autoinatic exchange may be converted to the sleeve supervision ofthe trunk board.

Relay D is provided so that ii'at any time a double or extended huntingoperation is required v between switching stagea'the sending out may 25-be held up beyond the normal interdigital pause,

In such a case battery will be reversed over-the negative and positiveOUT leads to the sender'i until such time as the hunting operation isconcludedandduringthis'time relay D will be operated since the.rectifier MR-F will be in a non-conductive direction. ,At armature di,Fig.

6, the circuit for relay IG-.and the magnet -im-,-

pulse springs IVES is opened and .the sending out of the trains ofimpulses is therefore holdup until relay D restores. 1

If the sender-is taken into use and not released v after a predeterminedperiod, 'the time delay relays TA and TB, Fig. 5, areoperated to'providesuitable alarms. When the sender is taken into use, relay BA atarmatureba t connects battery by way of resistanceYA to the upperwinding of. relay TA. The S and Z'leadsextending' from the upperwindings of-relays TA andTB are j common to a plurality of senders andconnect:

with a timingmechanismp if this mechanism. is in its normal position itwill extend on earth ation of the timing mechanism-the earth is removedfrom the S lead so that the TA relay i in another sender cannot beoperated if it is connected to the S lead during the timing of thepredetermined period and after this period has I elapsed the mechanismconnects earth to the 2 lead. This causes the operation of relay 'I'Bwhich thereupon looks over its armature t2)! and s at the" same armaturereleases relay TA} At armature tb-Z the battery potential to the upperwinding of relay TA is disconnected to prevent ice-operation of thisrelay when the timingme'chanism restores to normal asa' result of theremoval of. the earth-from the'ST lead, at armature 1123, Fig. (3, earthis applied to common lead l3yto' operate an alarm in the exchange; whileat armature tbd, Fig. 7, an interrupted. earth is connected over commonlead-Hi to flash a the sender supervisory lamp soas to bringto.

' It will be noticedthat on a call to a local the notice of the exchangemaintenance oflic'er which particular sender is faulty.

Considering now the function of relay BP, Fig. 6, which is connected inthe battery feed toall the switch driving magnets, if any switch shouldfail to home this-relay will be maintained operated and at armature bpl,Fig. 5, opens a point in the idle test circuit andconnects up relayTA tothe timing mechanism while at armature 19122 a holding earth is providedfor the relays TA and TB. Hence if relay BP is still operated at the endof the predetermined time interval an alarm will be given in the mannerdescribed in the previous paragraph and the taking into use of thesender willbe prevented.

Should it be required to cut the sender out of service temporarily fortest purposes, the busy I key will be operated whereupon at contactsKBl, Fig. 7, the sender supervisory lamp LP is lit and at'thesecontacts, contacts KBZ, Fig. 7,

and contacts K133, Fig. 6, the earth is removed giroin the variousholding leadsin the sender so that any relays already held operated arere-.

leased. On the release of the relay B, .a guard earth is applied to theincoming P conductor over key contacts K134 and armatureb't.

We claim: I

1. In a telephone system, trunk .lines for exswitching equipment forcont'rollingthe extension-of said calls, means for marking,in'saidequipment, these routes which are congested and have callswaiting, said marking for each-congested route varying in accordancewith the probable time required to complete said waiting calls andobtain a free trunk line in said route,

tending callsover one or more routes, automatic a calling station,means, at said calling station for seizing said equipment to extend acall over one of said routes'and for transmitting to said v equipmentcall-directing digits, and means in said equipment, eifective if saidone route: is congested and has calls. waiting, for automaticallyapprising the calling party of the probable length of delay before hiscall can be completed;-

' 2. In a telephone system,-trunk lines for extending calls over one ormore routes, automatic switching equipment for controlling theextnsionof said calls, means for characterizing, in

said equipment, those routes whiclr are-congested by heavy traffic andthe degree of said congestion,

means for seizing said equipment for the extenf sion of a callover oneof said routes and for transmitting thereto call-directing digits, andmeans in said equipment, effective if said one route has beencharacterized as congested, for

signalling the calling party accordingly, different signals beingreverted in accordance with the degree of congestion.

3.In a telephone system, trunk lines for extending calls over one ormore routes, a calling station, automatic switches over which said trunki lines are accessible to said station, meansfor transmittingcall-directing digits from said station to gain access, via saidswitches, to a trunk line in a particular route, signalling equipmenthavingmeans controlled by said digits, and means for characterizing, insaid equipment, those routes over which calls may not be completedwithoutv delay, said characterization varying in accordance withtheprobable length of said delay, said signalling means effective, ifsaid particular route is characterized, to signal the calling party toapprise him of the delay and the probable length thereof.

4. In a telephone system, trunk lines for extending calls over one ormore routes, a calling station, automatic switches over which said trunklines are accessible to said station, means for transmittingcall-directing digits from said station to gain access, via saidswitches, to a trunk line in a particular route, a register controlledby said digits, a switch controlled by said register and positioned in.accordance with certain of said digits, means operated over the wipersof .said last switch if calls may not be completed Without delay oversaid particular route, said last means being operated variably inaccordance with the probable length of delay, and means controlled bysaid last means to notify the subs'criber of the probable length of saiddelay.

5. A telephone system as claimed in claim 4,

wherein said switch is rendered effective only when one of the digitsreceived by said registeris of a predetermined value.

& 6. In a telephone system, trunk: lines for extending calls over one ormore routes, a calling station, automatic switches over which said trunklines are accessible to said station, means for transmittingcall-directing digits from said station to gain. access, via saidswitches; to a trunk line in a particular route, and means controlled bysaid digits for determining whether the call may be completed over saidparticular route without delay and, if not, for determining the probablelength of the delay, said last means thereupon effective, if said callmay not be completed without delay, to automatically notify the calling7. A telephone system as claimed in claim 6,

wherein said last means is eifective, only if said call may be completedwithout delay, to transmit impulses to said switches thereby controllingcertain of the same to give the calling station access to a trunk linein said particular route. 7

8. A telephone system as claimed in claim 6, wherein said last meansincludes sources of different tones and means selectively controlled inaccordance with the probable length of delay for reverting to thecalling party a particular one of the tones.

9. In a telephone system, trunk lines for extending calls over any of aplurality of routes, certain of said routes being alternative routes forothers of the routes, a calling station, automatic switches over whichsaid trunk lines are accessible to said station, means for transmittingcalldirecting digits from said station to gain access, via saidswitches, to a trunk line in one route, a register controlled by saiddigits, means associated with said register for determining thecondition of said one route and, at times, of an alternativeroute,'means for at times thereupon transmitting impulses to controlsaid switches in accordance with. said determination, and meanseffective at times if said call cannot be extended over either said oneroute or said alternative route without delay for determining theprobable length of said delay and for signalling the calling party inaccordance with the probable length thereof;

10. In a telephone system having trunk lines arranged in direct andalternative routes, a calling station, automatic switches over whichsaid trunk lines are accessible to said station, a register sender forcontrolling said switches, means for transmitting call-directing digitsfrom said station to control said register sender, means associated withsaid register sender efiective first to determine the condition of trunklines in a particular direct route and the corresponding alternativeroute in accordance with certain of the received. digits and thentocause said register sender to control said switches in accordance withsaid determination, thereby to extend a connection from said stationover said direct route or said alternative route, and means effectiveonly if one of the received digits is of any of certain predeterminedvalues for controlling said last means to prevent the extension of saidconnection over said alternative route.

11. In a telephone system having trunk lines arranged in direct andalternative routes, a calling station, automatic switches over whichsaid trunk lines are accessible to said station, a register sender forcontrolling said switches, means for transmitting call-directing digitsfrom said station to control said register sender, means saidalternative route, and means effective only if one of the receiveddigits isof any of certain predetermined values for causing said secondmeans to arbitrarily assume a predetermined condition of saidalternative route irrespective of the true condition ofthe same.

CHARLES EDMUND BEALE. IDRIS TREVOR RICHARDS.

